It is known to evacuate a coke oven chamber during the charging of coal into the same and to process the evacuated gas to recover coal dust and valuable components (byproducts) from the charging gas.
In the charging of coal into the chambers of a coke oven battery, it is common practice to provide a charging carriage upon the top or roof of the coke oven battery, this carriage being provided with a plurality of filling hoppers each of which can be aligned with an opening in the roof to charge the chambers in succession. It is also known to evacuate the resulting filling gas, which constitutes a gas-dust mixture, from the chamber during the filling process.
Especially when the charge consists of preheated coal, usually at a temperature up to about 250.degree. C., the filling gas which is displaced by the coal entering the coking chamber, contains large amounts of coal dust which is generally referred to in the industry as carryover.
It is important, on the one hand, that the gas/dust mixture not be released directly into the atmosphere because it contains toxic and pollutant components, and, on the other hand, to recover, for economic reasons, the relatively large amounts of carryover coal dust in the gas stream.
It has been determined that the charging of preheated coal into the chambers of a coke oven battery can result in evacuation of up to 1% of the charge in the form of coal dust with the evacuated gas. If, as is commonly the case, the chamber of a coke oven battery can receive a charge of up to 40 metric tons of coal, approximately half of a ton of coal may be lost by the entrainment thereof with the evacuated gas. Not only does this constitute a loss of a valuable component, but it generally overloads the particle separators, the gas coolers and the like and can even result in the formation of deposits in the tar separator, the gas cooler and the gas lines. Such deposits can interfere markedly with the overall effectiveness of the coking installation.
It has been proposed to overcome this problem, as much as possible, by preventing the charge from mixing with the evacuated filling gas. To this end, German patent DT-PS No. 541 754 discloses a system which eliminates the free fall of the coal into the chambers of the coke oven battery by introducing the coal with the aid of telescopically raisable and lowerable filling tubes so that the incoming coal is deposited as close as possible upon the bottom of the chamber or on the previously introduced coal.
In spite of such precautions, however, it is found in practice that portions of the filling gas are released into the atmosphere in an untreated manner to the detriment of the environment and that some significant quantities of coal dust are entrained with the gas which is released into the atmosphere.